{"id":1940,"date":"2009-11-08T16:15:25","date_gmt":"2009-11-08T23:15:25","guid":{"rendered":"http:\/\/multimedia.cx\/eggs\/?p=1940"},"modified":"2009-11-12T17:43:35","modified_gmt":"2009-11-13T00:43:35","slug":"state-of-the-art-compiler-optimization","status":"publish","type":"post","link":"https:\/\/multimedia.cx\/eggs\/state-of-the-art-compiler-optimization\/","title":{"rendered":"State of the Art Compiler Optimization"},"content":{"rendered":"

Felix von Leitner<\/a> delivered a talk at the 2009 Linux Kongress about the state of the art in compiler optimization (link to PDF slides)<\/a>. Presentation slides by themselves are not a good way to understand a talk and it would be better to learn if video for the actual talk is posted somewhere. Compiler optimization (or lack thereof) is fairly important to FFmpeg<\/a> developers.<\/p>\n

The talk analyzes how LLVM, icc, MSVC, Sun C, and gcc generate fast code in this day and age. One basic theme I gathered is that coders should forgo clever C optimizations as they tend to be counterproductive. I wish I could believe that, but there was that recent episode where I optimized FFmpeg’s Theora decoder by removing structure dereferences<\/a>. I’m sure that other performance-minded multimedia hackers will have other nits to pick with the broad generalizations in the presentation. I call your attention to the fighting words (which I have taken out of context since it’s such a fun quote) on slide 41: “Note: gcc is smarter than the video codec programmer on all platforms.”<\/strong> Further, slides 53-55 specifically call out madplay<\/a> for inline ASM that allegedly didn’t improve efficiency vs. what the compiler could achieve with the raw C code.<\/p>\n

On the whole, the findings are probably quite accurate for the kind of C code that most people need to write (e.g., “No need to write a >> 2 when you mean a\/4!”). <\/p>\n

Speaking of compilers, FATE<\/a> now covers Intel’s 11.1 series C compiler for both 32- and 64-bit icc. I have also updated the stale snapshots of the gcc-svn for my machines (I still need to write a tool to do that for me automatically and continuously).<\/p>\n","protected":false},"excerpt":{"rendered":"

Where we are in the battle of compiler-automated vs. hand-tuned program optimization<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[101,28],"tags":[],"class_list":["post-1940","post","type-post","status-publish","format-standard","hentry","category-fate-server","category-programming"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t